Abstract: The uniaxial compression process of granite is monitored by acoustic emission and thermal infrared technology, and the variations of acoustic emission and infrared radiation during rock fracture are analyzed. On this basis, the analytical expressions of rock damage variables are derived from the perspectives of internal damage and surface damage. According to the complementarity of these two at different stages, a piecewise curve damage model based on sound-heat is established to study the damage evolution characteristics of rock under uniaxial compression. The results show that: (1) The damage evolution process of rock can be divided into three stages: initial damage stage, stable damage stage and accelerated damage stage. In the initial damage stage, neither internal damage nor surface damage develops. In the stable damage stage, the micro-damage in rock accumulates continuously, but there is no development on the surface damage. In the accelerated damage stage, both the internal damage and the surface damage increase rapidly. Compared with the increase in internal damage, the abnormal increase in surface damage occurs earlier. (2) By comparing the stress-strain curves calculated from the comprehensive damage variables with the experimental curves, it is found that the trend of the two curves is approximately the same. The comprehensive damage variables defined are reasonable and can better reflect the progressive evolution of crack defects in rock from generation, development to failure.

Key words: granite uniaxial compression, infrared radiation, acoustic emission, damage evolution